Broadband wireless access may be used to provide mobile wide area network access (e.g., Internet access) to locations that may or may not have wired network access. A set of standards that define a strategy for broadband wireless access include IEEE 802.16, which is often referred to a WiMAX, includes standards for various elements that may be used to provide broadband wireless access.
IEEE 802.16 standards refer to, for example, Draft Standard IEEE P802.16-2004, “Standard for Local and Metropolitan Area networks—Part 16: Air Interface for Fixed Broadband Wireless Access Systems,” Draft Standard IEEE P802.16e/D12, “Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands,” and Draft Amendment-IEEE 802.16g-05/0008r1, “Amendment to IEEE Standard for Local and Metropolitan Area Networks—Management Plane Procedures and Services,” as well as related documents.
Most initial WiMAX deployments will be Point to Multipoint (PMP) networks based on centralized scheduling and radio resource management in the base station (BS). The implication of this is that the BS may be required to schedule grants on the uplink (UL) for the remote station (RS) to transmit. In a typical mobile/fixed WiMAX deployment, a RS may have multiple types of applications running concurrently. Different applications may require potentially different PER (Packet Error Rate) targets. Based on the UL signal to noise ratio (SNR) of the RS, these different PER targets translate to different Modulation coding schemes (MCS) on the UL. The UL MCS is called UIUC (Uplink Interval Usage code).
Hence, a RS may use different UIUC for different applications or potentially even for the same application. As an example, a single video stream may be split into multiple streams having associated connection identifiers (CIDs) with different error rates. If MPEG encoding is used, the I frames on CID1 may have a different packet error ratio (PER) and a less efficient UIUC and the B/P frames on CID2.
Another example could be a RS running a file transfer based on TCP and a latency sensitive streaming application simultaneously on two different CIDs. The TCP connection can operate at a PER as high as, for example, 30%, because it is not extremely delay sensitive, and the underlying MAC layer retransmission mechanism (ARQ/HARQ) can correct the errors reduce the residual error rate. However, for the latency sensitive streaming application, the ARQ cannot operate due to latency constraints—implying that the PER should be much lower—say 1-5%.
IEEE 802.16 standards provide grants for the RS for UL transmission in the UL map information elements (IEs). Each IE represents an allocation to a particular RS and specifies the number of UL slots for this allocation, the beginning and ending offsets for this allocation, so that the RS can uniquely identify the allocation. All of the allocations to the RS, happen on the “Basic CID” (which is equivalent to a common control connection) of the RS.
The RS will not be able to able to decode the PER associated with the UL grants and may use the grant with the higher PER for the application that requires the lower PER. This may exacerbated by the fact that the UL channel may changing and the RS my not be able to adapt efficiently to the changes because the BS processes the UL signals, except for the time-varying UIUC values allocated by the BS in the UL grants.